Phase I strains 18-323, Tohama and L-84 of produced paroxysmal coughing when encased in agarose beads and administered intrabronchially to adult Sprague-Dawley rats. In contrast, the Phase IV variant of strain L-84 was inactive in cough induction, as was strain BP 357, a transposon-insertion mutant which is deficient only in pertussis toxin (PT). Strain BPM 1809, which lacks only the heat-labile toxin, was similar to the unmodified Phase I strains for cough induction, indicating that this toxin is not needed to induce coughing. also was inactive as a cough inducer. These results indicate that PT, present in Phase I strains of , and absent from Phase IV strains, strain BP 357 and , is essential for the induction of paroxysmal coughing in this rat model of whooping cough. Prior injection of DTP (whole-cell) vaccine greatly reduced the incidence of coughing in rats challenged subsequently with Phase I . Serological responses were monitored after intrabronchial infection with the various bacterial strains and after vaccination and challenge. The PT-positive or -negative status of the strains was confirmed by the appropriate presence or absence of anti-PT IgG in the convalescent sera.


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